WAV to Base64

How to convert WAV to Base64

1. Drop a .wav file on the box or pick it with the file picker.
2. Play it in the preview.
3. Output as is set to Data URI. For APIs choose Plain Base64, or JSON to include the name, MIME type and size.
4. Press Copy output. Recordings of more than a few seconds are long strings; Save as .txt is easier to handle.

How big a Base64 WAV gets

Uncompressed PCM is easy to calculate: sample rate × bytes per sample × channels gives bytes per second. Add the standard 44-byte header and multiply by 4/3 for Base64:

Files recorded by some apps have extra chunks with metadata, so real sizes can be slightly larger.

WAV and speech APIs

Speech recognition services commonly accept uncompressed 16-bit PCM because it decodes without loss and needs no codec. When they take audio inline in a JSON request, it goes in as Base64, along with fields that describe the encoding, sample rate and channel count. Those values must match the file. A 44.1 kHz stereo recording declared as 16 kHz mono produces garbage transcripts or an error.

Speech models typically work at 16 kHz mono or lower. Converting a CD-quality stereo recording to 16 kHz mono before encoding makes the request about five and a half times smaller, usually without hurting recognition. Do it in an audio editor or with a command-line converter; this page encodes the file as it is.

If the inline limit is still too small for a long recording, these services usually also accept a link to a file in storage, which avoids Base64 entirely.

Generate a WAV and encode it in Python

The standard library can write a WAV and encode it, which is handy for test fixtures. This makes a 200 ms beep at 880 Hz:

import base64, io, math, struct, wave

rate = 8000
samples = b"".join(
    struct.pack("<h", int(12000 * math.sin(2 * math.pi * 880 * i / rate)))
    for i in range(rate // 5)
)
buf = io.BytesIO()
with wave.open(buf, "wb") as w:
    w.setnchannels(1)
    w.setsampwidth(2)
    w.setframerate(rate)
    w.writeframes(samples)

uri = "data:audio/wav;base64," + base64.b64encode(buf.getvalue()).decode()

The file is 3,244 bytes and the data URI 4,350 characters, starting data:audio/wav;base64,UklGRqQMAABXQVZF. More on files and streams in Base64 in Python.

Going back

Base64 to WAV plays a Base64 WAV string and saves it as a file. To shrink audio for the web, use a compressed format; see MP3 to Base64 for size comparisons.

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